1. Field of the Invention
The present invention relates to information processing apparatuses using class-classification adaptive processing.
2. Description of the Related Art
Variable-length encoding, typical of which is entropy encoding, has been used in many data-transmission compression methods to increase the compression rate. A feature of entropy encoding is that the lengths of code words are changed according to the content of data to be compressed, to implement compression. For example, a short code word is assigned to data which is frequently used, and a long code word is assigned to data which is used not frequently. As a result, the amount of information of the entire data to be transmitted is reduced.
When a receiving side receives erroneous data due to a communication error, since the length of each code word is always changed according to the content of the data, an error in decoding continues to a point which is used as a transmission-data reference. This phenomenon is called “error propagation.”
In moving-picture compression methods, typical of which is Moving Picture Experts Group methods (MPEG methods), discrete cosine transform is used to reduce spatial redundancy and only differences between frames are transmitted to reduce redundancy in time in order to reduce the amount of data.
Moving-picture data compressed by such a compression method is decompressed at the receiving side. When transmitted moving-picture data lacks its part due to a communication error or for some reason, the missing part is expanded in space and in time, and its effect is prominent at a higher compression rate.
Since a communication path in a mobile environment is poor compared with that of a fixed station or that in wire environment, burst data missing called “packet loss” occurs relatively frequently. Therefore, an enhanced error-correcting code is employed in image communication which uses compression, to prevent data from being lacked in a communication path in such a mobile environment.
If there is a missing pixel which cannot be restored by the error correcting code, correlation between the missing pixel and its surrounding pixels is analyzed and pixels disposed in a direction in which strong correlation is found are used for linear interpolation. The missing pixel may be simply replaced with a pixel disposed in a direction in which strong correlation is found. Alternatively, the amount of motion or the motion vectors of the surrounding pixels are detected and pixels disposed in a direction in which strong correlation is found are used for linear interpolation. The missing pixel may be concealed by using a median filter.
When the missing pixel is replaced with another pixel or linear interpolation is used for the missing pixel, however, since resolution decreases and continuity with surrounding pixels is lost, a reproduced image gives a different impression. Also in a case in which a median filter is used, an incongruous impression is given.